1. Field of the Invention
The present invention relates to an apparatus for coating a plate-like workpiece with a solution, and more particularly to a solution coating apparatus for use in the manufacture of liquid crystal displays (LCD) or the like.
2. Description of the Relevant Art
One modern display device that the image display industry has been making efforts to develop as a promising substitute for the conventional cathode-ray tube is a liquid crystal display which comprises a liquid crystal sandwiched between two glass substrates each composed of devices and electrodes that make up a plurality of pixels on its surface. According to the prevailing liquid crystal display design, the pixels are arranged in an active matrix drive system in which they are driven by devices such as thin-film transistors (TFT) or metal-insulator-metal (MIM) devices.
Thin-film transistors or other drive devices are fabricated on glass substrates by the semiconductor fabrication technology also used for fabricating integrated circuits on silicon wafers. The semiconductor fabrication process comprises a number of steps which includes the step of coating a resist solution on a glass substrate. In the coating step, a resist solution is dropped on a glass substrate that is set by a vacuum chuck in an inner cup, and then the vacuum chuck and the inner cup are rotated in unison with each other by a spinner for centrifugally forming a uniform coating of resist solution on the surface of the glass substrate.
When a glass substrate is to be set on or an uncoated glass substrate is to be removed from the vacuum chuck, the peripheral edge of a lower surface of the glass substrate is supported by a manipulator or the like so that the upper surface of the glass substrate remains untouched. To allow the manipulator or the like to support the peripheral edge of the lower surface of the glass substrate, it is necessary that a clearance be defined between the glass substrate and the bottom of the inner cup for the manipulator or the like to enter while the glass substrate is being placed on the vacuum chuck.
To meet such a requirement, it has been customary for the vacuum chuck to be smaller in diameter than the glass substrate, so that the glass substrate has its peripheral edge projecting radially outwardly of the vacuum chuck.
While the resist solution is being applied to the glass substrate, the glass substrate and the inner cup are rotated in unison with each other. However, the clearance which is present between the glass substrate and the bottom of the inner cup produces turbulent air flows, making the coating thickness irregular or forcing the resist solution around the peripheral edge to the lower surface of the glass substrate.